Semiconductor optical devices are broadly fall into light-emitting devices and light-receiving devices. Known light-emitting optical devices include semiconductor light-emitting diodes (LEDs) which emit light having a specific wavelength from infrared to ultraviolet as a center wavelength. Further, known light-receiving semiconductor optical devices include semiconductor light receiving devices which convert optical signals and light energy into electrical signals and solar cells which convert light energy such as solar light into electrical energy.
Of these semiconductor optical devices, for example, light-emitting semiconductor light-emitting diodes emit light by converting electric current flown through p-n junctions into light energy. As a means to improve the light emission efficiency of semiconductor light-emitting diodes, there is a demand for a technique for improving the extraction efficiency of light emitted from a light emitting layer in a semiconductor layer.
In light receiving semiconductor light receiving device and solar cells, light received at pn junctions is converted into electrical energy due to the photovoltaic effect, and the resultant electrical energy is used in the applications such as photodetectors and generation of electrical power. There is a demand for a technique for improving light harvesting efficiency in order to increase the collection efficiency or sensitivity for semiconductor light receiving devices, and in order to increase the light conversion efficiency for solar cells. Surface roughening of a light emitting surface and a light receiving surface is known as such a technique for improving light extraction efficiency or light collecting efficiency.
For example, JP 2011-100829 A (PTL 1) discloses a method of manufacturing a semiconductor light-emitting device comprising immersing, in an aqueous solution of nitric acid, a semiconductor laminate having a light emitting layer and a surface layer which includes a Ga(1-x)AlxAs layer (0≤x<0.8) and through which light emitted from the light emitting layer is extracted, thereby roughening the surface of the surface layer. According to the technique of PTL 1, a semiconductor light-emitting device with increased light output can be manufactured by improving the efficiency of light extraction from inside the semiconductor crystal.
JP 2001-004442 A (PTL 2) discloses an infrared sensor including an infrared transmitting unit and an infrared detecting unit with the outer surface of the infrared transmitting unit being an uneven plane.
For example, a semiconductor light-emitting diode typically has a semiconductor laminate including an n-type semiconductor layer, a light emitting layer (also referred to as an active layer), and a p-type semiconductor layer, the semiconductor laminate being electrically sandwiched between a pair of electrodes. Such a semiconductor light-emitting diode is disclosed in JP 2007-258326 A (PTL 3). Specifically, the semiconductor light-emitting diode includes a conductive support substrate; a metal layer and a light emitting portion composed of an InGaAlP-based semiconductor including an n-type cladding layer, an active layer, and a p-type cladding layer on the conductive support substrate, in which a current diffusion layer is provided on the light emitting portion and a surface of the current diffusion layer opposite to the surface in contact with the light emitting portion is a light extraction surface. In the semiconductor light-emitting diode, a thin connection pattern is formed in which a first ohmic wiring electrode portion is formed between the metal layer and the light emitting portion, a pedestal electrode and a second ohmic wiring electrode portion are provided on the light extraction surface, and the pedestal electrode and the second ohmic wiring electrode portion are electrically connected.